This invention relates to a modified derailleur for a multi-speed bicycle, and more particularly to a modified derailleur that is useful to prevent the chain from disengaging from the rear sprockets when the bicycle is used in rough terrain such as off road or mountain biking.
A typical derailleur is used to effect gear changes in a multi-speed bicycle. For example, in a ten speed bicycle, there are typically two different size chainwheels mounted on the crank spindle adjacent the pedals of the bicycle. Along the axle of the rear wheel, five sprockets of varying sizes are laterally mounted next to one another. The bicycle chain spans a particular chainwheel and a particular sprocket thereby effecting a particular gear ratio between the pedals and the rear wheel. Different combinations of the two chainwheels and the five rear sprockets results in ten possible gear ratios, thus a ten-speed bicycle.
A derailleur is used to provide a mechanism to move the bicycle chain from one of the rear sprockets to another of the rear sprockets thus changing the gear ratio of the bicycle. A gear lever is connected by a cable to the gear changer. When the rider desires to change to a higher gear ratio, the rider moves the gear lever which causes the cable to pull the derailleur outward against the action of a spring and the chain is shifted to a smaller sprocket. To change to a lower gear ratio, the derailleur is allowed to move inward by the action of the spring and this moves the chain to a larger rear sprocket.
It is detrimental to the normal operation of a bicycle to have the bicycle chain become disengaged from either the chainwheel or the rear sprocket. A standard derailleur uses a torsion spring at each of two vertical pivot points to place the chain under tension so that the chain will not inadvertently disconnect from the rear sprocket. The torsion springs must be strong enough to prevent this inadvertent movement, but not so strong as to prohibit the movement of the chain when shifting is desired.
Chain oscillation or chain play occurs when the bicycle is subject to a shock or a jolt such as would be encountered when the bicycle is being ridden over rough terrain as would normally be encountered in an off-road or mountain biking situation. If the shock or jolt is severe enough, the torsion springs will not hold the chain on the rear sprocket and the chain will come off resulting in the bicycle becoming inoperable. It is possible however to overcome this undesirable characteristic of standard derailleurs.
It is an object of the present invention to provide a positive locking mechanism to each of the two vertical pivot points of a derailleur assembly to prevent inadvertent chain oscillation or chain play when the derailleur encounters shocks or jolts from off-road or mountain biking.
It is a feature of the present invention to utilize a band lock or a ratchet lock on the pivot points, such as the rotating drum, of the derailleur to hold the derailleur securely in place. The band lock or ratchet lock is then released prior to shifting by activating a lever attached to the handle bars to permit the shifting to occur. Once a change in gear ratio has been achieved, the band lock or ratchet lock is reapplied by use of the lever to once again securely hold the derailleur during riding over rough terrain.
It is an advantage of the present invention that a derailleur is modified to prevent unwanted chain oscillation or chain play to increase the ability of a bicycle rider to traverse rough terrain often encountered in off-road or mountain biking situations.